This invention relates to dynamoelectric machines in the form of electric motors. While the invention is described with particularity with respect to brushless permanent magnet motors (BPM), those skilled in the art will recognize the wider applicability of the inventive principles disclosed hereinafter.
There has been, and continues to be, a movement toward high operating efficiency devices in electrical designs. That movement includes a move by appliance manufacturers to provide high efficiency consumer appliances for general use. Certain improvements in such appliance efficiency are more obvious than others. For example, the ubiquitous household refrigerator has at least three electric motors associated with it. They include a hermetic compressor motor which drives the compressor for the refrigerant system, an evaporator motor, and, in many refrigerators, a condenser motor. The general operation of the refrigeration system of the conventional refrigerator is well known. The compressor moves the refrigerant from the evaporator into the condenser. It then forces the refrigerant back to the evaporator through an expansion valve. Refrigerant vapor leaves a compressor at high pressure. As it flows into the condenser, the high pressure causes the vapor to condense back to liquid refrigerant. As this happens, the vapor gives out heat, making the condenser warm. The condenser is at the back of the refrigerator, and heat flows into the air around the refrigerator, often with the aid of the aforementioned condenser fan. The refrigerant leaves the expansion valve at low pressure, causing it to evaporate inside the pipe and get cold. The evaporator is inside the refrigerator and heat flows into the evaporator, making the refrigerator cold. Again, a fan is used to force air over the evaporator and distribute the cool air throughout the refrigerator interior.
Refrigerators operate day and night and because of that operation, their operation cost is relatively substantial, even when attempts are made to increase their efficiency. Recently, there has been an industry-wide effort by refrigerator OEMs (original equipment manufacturers) to raise the level of refrigerator efficiency.
As will be appreciated by those skilled in the art, brushless permanent magnet motors in operational use offer the best efficiency presently known for electric motors in general use, although switched reluctance motors (SRM) and controlled induction motors (CIM) often are configured to achieve substantially equivalent performance. In the size of the motor of this invention, the brushless permanent magnet motor was found to offer the best engineering solution. A brushless permanent magnet motor is similar to other motor types in that it includes a stator assembly having a core of laminations formed from suitable magnetic material. The core has winding receiving slots formed in it. The rotor assembly commonly is the component that distinguishes a permanent magnet motor from other motors. Unlike other conventional motor constructions, a BPM rotor has at least one permanent magnet associated with it. The motor may be either of a conventional design, in which the stator assembly has an axial opening through the core for reception of the rotor assembly, or the motor can be a so called inside out motor, which has the rotor assembly outboard of the stator.
While brushless permanent magnet motors offer higher efficiencies, they require an electronic circuit for applying electrical energy to the motor windings for proper operation of the motor. The control circuits required for motor operation often make application of the permanent magnet motor economically unjustifiable.
Condenser and evaporator fans in refrigerators conventionally are small and low cost designs. The low cost design of these motors commonly equates with a relatively low efficiency design. We have found that the lower efficiency evaporator or condenser motors can be replaced with more efficient permanent magnet motors when the assembly and construction techniques disclosed hereinafter are employed for and in the motor design, and the motor control functions are accomplished in accordance with the various disclosures incorporated by reference. One of the objects of this invention is to provide an economically producible permanent magnet condenser motor.
Another object of this invention is to provide a motor design which can be incorporated into a variety of applications.
Another object of this invention is to provide a motor construction which has an integrally formed blade assembly.
Another object of this invention is to provide a motor blade assembly which is electrically insulative.
Yet another object of this invention is to provide a motor blade combination which is protective of the motor and associated controls.
Still another object of this invention is to provide an integral fan blade design which can be easily modified for different customer requirements.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.